1. Field of the Invention
The present invention relates to a nitride-based compound semiconductor light emitting device capable of emitting light in the blue to ultraviolet range, and a fabricating method thereof. More particularly, the present invention relates to a nitride-based compound semiconductor light emitting device having a conductive substrate bonded thereto and a fabricating method thereof.
2. Description of the Background Art
A nitride-based compound semiconductor, represented by InxGayAlzN (x+y+z=1, 0≦x<1, 0<y≦1, 0≦z<1), for example, has a large energy bandgap and high thermal stability, and allows control of the bandgap width by adjusting composition thereof. Accordingly, the nitride-based compound semiconductor has attracted attention as a material that can be applied to various kinds of semiconductor devices, such as a light emitting device, a high-temperature device and others.
In particular, as for a light emitting diode using the nitride-based compound semiconductor, a device having luminous intensity of some cd grades in the blue to green wavelength range has already been developed and brought to practical use. As for a pickup light source for large-capacity optical disk media, practical application of a laser diode using the nitride-based compound semiconductor is becoming an objective of research and development.
Japanese Patent Laying-Open No. 09-008403 discloses a device structure of such a laser or light emitting diode. Specifically, as shown in FIG. 5, on a conductive substrate 100 having a positive electrode 107 formed, a first ohmic electrode 102 and a second ohmic electrode 101 are formed. A P-type layer 103 of gallium nitride-based semiconductor, an active layer 104 and an N-type layer 105 are stacked successively thereon, and a negative electrode 106 is formed further thereon. Here, first ohmic electrode 102 and second ohmic electrode 101 are bonded together by hot pressure bonding.
As such, in the conventional technique as described in Japanese Patent Laying-Open No. 09-008403, an ohmic electrode is formed on a conductive substrate, and hot pressure bonding or the like is used for bonding of the gallium nitride-based semiconductor layer.
With such a technique, however, the conductive substrate may peel off from the ohmic electrode due to poor adhesion therebetween. If the conductive substrate and the ohmic electrode are separated from each other completely, it is not possible to remove a sapphire substrate, hindering formation of a light emitting device. If they are partially separated from each other, flow of the current from the gallium nitride-based semiconductor layer to the conductive substrate will be difficult, leading to an increase of operating voltage, thereby causing degradation in reliability of the light emitting device.
Further, the partially peeled-off state will cause penetration of solvent, resist, or etchant during the process. For example, upon fabrication of a lamp light emitting device, resin, water or the like will enter through the peeled-off part, which will expand the peeling, possibly destroying the ohmic electrode. This would degrade reliability of the light emitting device.
Still further, when Au wire is bonded to a pad electrode, if adhesion between the conductive substrate and the ohmic electrode formed thereon is poor, there will occur peeling of the conductive substrate from the ohmic electrode, thereby causing an increase of operating voltage.